A new technique for the continuous assessment of fetal and neonatal cardiac performance

Abstract

A paucity of informaion exists concerning the intrinsic physiologic properties of the developing heart. Accordingly, new methods have been developed to evaluate fetal and neonatal cardiac performance in situ in the chronically instrumented fetal and newborn lamb. Sonocardiometry provides a continuous recording of internal left ventricular dimensions. Pressures are monitored from the carotid artery, superior vena cava, left atrium, and left ventricle. The heart may be paced with bipolar pacing wires sutured to the left atrium. A 14 day recovery period is allowed piror to hemodynamic study. The instrumentation does not prevent the spontaneous vaginal delivery of fetuses and their subsequent postnatal study. The recorded physiologic data allow the calculation of left ventricular volume, ejection fraction, velocity of circumferential fiber shortening, myocardial pressure-volume relations, force-velocity relations, peripheral resistance, and left ventricular cardiac output. Basal data are presented in this report. The percentage shortening of the left ventricle of the fetus was similar to adult values, whereas velocity of shortening and maximum rate of pressure rise were significantly less than in the adult. A striking finding in the immediate postnatal period was a doubling of the left ventricular output shortly after birth with an associated increase in cardiac dimensions.